In general, soft magnetic components, also known as cores, of electrical motors and machines are made of insulated thin sheets of soft magnetic materials, e.g. iron or electrical steel. These insulated thin sheets of soft electrical material are also known as laminations. Cores are made of laminations in order to reduce the appearance of eddy currents and, thus, increase the efficiency of the electrical motors and machines.
In linear motors having ring shaped stator cores and tubular movers, wherein a mover is the portion of the linear motor that is to be moved by means of interaction with a magnetic field of a stator, each metal sheet is arranged in radial and axial plane in order to minimize the effect of eddy currents.
In some linear motors metal sheets are stacked together in parallel forming a core portion which is arranged so that one metal sheet is in the radial axial plane and the others are parallel to that one.
One problem with stator cores made as described above is that the coil has to be wound into a slot of the stator core. This is especially troublesome when the opening of the slot is arranged at an inner circumferential surface of the stator core.
Further, the linear motors utilizing the above mentioned techniques are not efficient in regard of the ratio of produced force to the total spatial volume of the linear motor, i.e. produced force/spatial volume.
Accordingly, there is a need for linear motors producing a specific force but with a smaller spatial volume and for stators that is easier to provide with coils.
In U.S. Pat. No. 6,060,810 there is presented a stator for a linear motor, said stator having staggered core lamination. The stator includes a stator coil that is wound in a cylindrical shape and L-shaped lamination sheets having one horizontal unit and one vertical unit. The horizontal unit of a plurality of lamination sheets are alternately laminated in a radial shape on the upper and lower surfaces, thus forming a cylindrical shape.
When building such a stator there is no need to wind the coil through an opening to the slot of the stator core. However, it may be complicated to build the stator core on to the coil.
Further, a stator core according to U.S. Pat. No. 6,060,810 is still not really efficient when it comes to the ratio of produced force to the spatial volume of the motor.